http://www.paper.edu.cn Catalysis Communications 7 (2006) 979–981 www.elsevier.com/locate/catcom Highly regioselective hydroaminomethylation of long chain alkenes catalyzed by Rh–BISBIS in a two-phase system Yingyong Wang, Junhua Chen, Meiming Luo *, Hua Chen, Xianjun Li Key Laboratory of Green Chemistry and Technology of Ministry of Education at Sichuan University, College of Chemistry, Sichuan University, Chengdu, Sichuan 610064, PR China Received 5 October 2005; received in revised form 17 January 2006; accepted 12 April 2006 Available online 22 April 2006 Abstract The hydroaminomethylation of long chain alkenes with secondary amines in aqueous/organic two-phase system catalyzed by rho- dium catalyst precursor and water-soluble diphosphine ligand BISBIS (sulfonated 2,20-bis(diphenylphosphinomethyl)-1,10-biphenyl) was investigated. The result showed that the use of BISBIS improved the reaction activity and especially regioselectivity for linear amine significantly compared with the monophosphine ligand TPPTS [P(m-C6H4SO3Na)3], the ratio of linear to branched amine was up to 83. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Hydroaminomethylation; Long chain alkene; Rh complex; Aqueous two-phase catalysis 1. Introduction two-phase catalytic system [6]. We reported that the cata- lytic hydroaminomethylation in aqueous/organic two- Amines with long aliphatic chains are of importance as phase system could be extended to long chain alkenes by synthetic intermediates for surfactant, membrane compo- using water-soluble rhodium catalyst RhCl(CO)(TPPTS)2 nent and biologically active compounds [1]. Hydroami- in the presence of cationic surfactant cetyltrimethylammo- nomethylation, the one-pot efficient synthesis of amine nium bromide (CTAB) [7]. Though good conversion and with alkene, amine (or ammonia) and synthetic gas repre- chemoselectivity for amines were obtained, the regioselec- sents one of the most elegant synthesis of this class of com- tivity for linear amine remains to be further improved. pounds. Since the discovery by Reppe et al. in 1949 [2], the Here we report our recent progress in the high regioselec- hydroaminomethylation reaction has attracted much atten- tive hydroaminomethylation of long chain alkenes with tion. The classical hydroaminomethylations are generally secondary amines using Rh–BISBIS complex as catalyst carried out in homogeneous catalysis system [3–5], where in aqueous/organic biphasic system. the difficulties of the catalyst recovery and catalyst separa- tion from the product constitute major drawbacks. Possible 2. Results and discussion solutions to these problems include ‘heterogenizing’ a homogeneous catalyst, either by anchoring the catalyst According to the mechanism of hydroaminomethyla- on a support, or by using a liquid–liquid two-phase system. tion of alkenes, the reaction process consists of three main In 1999 Beller and co-workers investigated the hydroami- steps: initial hydroformylation of an alkene, followed by nomethylation of lower olefins (6C5) in aqueous/organic condensation of the intermediate aldehyde with a primary or secondary amine to form an enamine or imine, and * Corresponding author. then a final hydrogenation to give a saturated secondary E-mail address: [email protected] (M. Luo). or tertiary amine [8,9]. It is known that the use of 1566-7367/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2006.04.010 转载 中国科技论文在线 http://www.paper.edu.cn 980 Y. Wang et al. / Catalysis Communications 7 (2006) 979–981 diphosphine ligand BISBI (2,20-bis(diphenylphosphinom- ethyl)-1,10-biphenyl) in the homogeneous hydroformyla- tion of alkenes affords high regioselectivity for linear aldehyde [10,11]. We envisioned that the use of water-sol- Scheme 1. Equilibrium between rhodium complexes. uble diphosphine ligand BISBIS would also exhibit high activity and excellent regioselectivity for linear tertiary amine in the hydroaminomethylation of long chain alk- We also investigated the hydroaminomethylation reac- enes. The results summarized in Table 1 showed that high tion of alkenes of different chain length with other second- regioselectivity for linear amine was indeed obtained in ary amines such as piperidine, morpholine, diethylamine the hydroaminomethylation of 1-dodecene with dimethyl- and dipropylamine. As shown in Table 2, except for the amine in aqueous/organic two phase using the catalyst case of dipropylamine, excellent conversion, regioselectiv- system: RhCl(CO)(TPPTS) -BISBIS-CTAB. 2 ity and good chemoselectivity for tertiary amines were With a lower molar ratio of BISBIS to rhodium ([BIS- obtained. The regioselectivity for linear amines increased BIS]/[Rh] = 2.5:1), the regioselectivity for linear amines with the chain length of the alkene and the steric hindrance (L/B: the ratio of linear to branched tertiary amine) of the secondary amines. Bulky starting secondary amines increased significantly from 14.6 to 44.6 and the chemose- showed lower chemoselectivity for the formation of tertiary lectivity for amines increased from 46% to 70% as com- amines owing to more hydrogenation and isomerization pared with the case of only using TPPTS as ligand side reactions. Morpholine, which is more basic and nucle- ([TPPTS]/[Rh] = 30). Both the chemoselectivity and regi- ophilic than diethylamine, gave better selectivity for amines oselectivity for linear amine increased with the increasing [9]. of the ratio of [BISBIS]/[Rh]. When the ratio of [BIS- BIS]/[Rh] was over 5, the conversion of alkene and the chemoselectivty for amines held nearly constant, but the 3. Experimental regioselectivity for linear amines increased to the value of 98.8% (L/B = 83.8). Rhodium complexes RhCl(CO)(TPPTS)2 and water- It can be supposed that the in situ-formed catalytic soluble phosphine ligand BISBIS were synthesized in active species of the rhodium catalyst system with BISBIS our laboratory according to the literature [14,15].1- as ligand in hydroaminomethylation were similar to those Alkene (Fluka), CTAB (AR) and other reagents (AR) in hydroformylation [12]. There is an equilibrium between were commercially obtained and not treated further. two species 1 and 2 as shown in Scheme 1. The large Water was doubly distilled. Synthetic gas was obtained increase of activity and L/B ratio could be attributed to by directly mixing carbon monoxide (99.9%) and hydro- that the equilibrium of ligand exchange was shifted to gen (99.9%) with the ratio of 1:1. GC analysis was per- species 2 and the diphosphine chelated rhodium complex formed on HP 1890II equipped with an FID (hydrogen became the predominant catalytic active species. Accord- flame ionization detector) and a capillary column SE-30 ing to the literature [13], a strong correlation was found (30 m · 0.25 mm). NMR spectra were recorded on a Var- between regioselectivity for linear product and natural ian INOVA 400 MHz or Bruker AC-E 200 MHz NMR bite angle of diphosphine ligand. Ligand like BISBI with spectrometer. Mass spectra (GC–MS) experiments were a wide natural bite angle of 113° and a moderate flexibil- conducted on Agilent-6890. ity might preferentially coordinated diequatorially with a A representative procedure for catalytic hydroaminome- metal (ee configuration), which could be sterically and thylation is as follows (entry 4, Table 2): catalyst precursor electronically favorable for the formation of linear com- RhCl(CO)(TPPTS)2 (0.2 mol %), BISBIS (1 mol %), CTAB pounds [10,11]. (0.01 mol/l), 1-dodecene (5 mmol), dimethylamine solution Table 1 Effect of molar ratio of BISBIS to rhodium on the hydroaminomethylation of 1-dodecenea [BISBIS]/[Rh] Dodecane (%) Isomerized dodecenec (%) Aldehyde (%) Conversion (%) Selectivity for amine (%) L/B (amine) LB 30:1b 14.2 7.3 5.1 22.8 91.4 46.1 14.6 1:1 20.8 9.1 9.5 12.8 91.7 43.1 22.2 2.5:1 16.6 6.9 1.5 2.9 96.3 70.2 44.6 5:1 11.2 4.4 1.0 1.5 96.5 81.2 70.3 7.5:1 10.8 4.7 0.9 1.1 97.0 81.9 78.5 10:1 12.5 5.5 1.0 1.3 96.6 79.2 83.8 a À3 Reaction conditions: [Rh] = 1.8 · 10 mol/l; dimethylamine:dodecene = 4:1; CTAB 0.01 mol/l; CO:H2 = 1:1; P = 3 MPa; T = 130 °C; t =5h. b TPPTS as ligand without addition of BISBIS. c Produced as byproduct in the reaction. 中国科技论文在线 http://www.paper.edu.cn Y. Wang et al. / Catalysis Communications 7 (2006) 979–981 981 (20 mmol) and water (3.5 ml) were added in a 60 ml stain- less steel autoclave equipped with a magnetic stirrer. The autoclave was purged three times with synthetic gas and 60.9 70.1 71.0 L/B (amine) 63.8 70.3 74.9 34.1 40.4 42.6 charged to 3 MPa, and reacted for 5 h at 130 °C, and then the autoclave was quickly cooled to ambient temperature. The solution automatically separated into two layers after a few minutes. The upper organic layer was clear colorless, and the lower aqueous layer containing the catalyst and ligand was brown-yellow. After separated in a separatory funnel, the products in the organic phase were analyzed 71.9 66.8 46.8 amine (%) 74.1 81.2 70.8 84.4 82.8 80.0 by gas chromatography. The linear and branched amines were purified by column chromatography (silica gel) for characterization. =5h. N,N,2-trimethyl-1-dodecanamine [3]:C15H33N (entry 4, t 1 Table 2, branched amine) H NMR (400 MHz, CDCl3)d C; ° 2.20 (s, 6H), 1.99–2.10 (m, 2H), 1.55–1.60 (m, 1H), 1.22–1.40 (m, br, 17H), 0.98–1.10 (m, 1H), 0.81–0.89 (m, = 130 13 Conversion (%) Selectivity for T 6H). C NMR (50 MHz, CDCl3)d 67.25, 45.64, 35.14, 31.66, 30.96, 29.93, 29.64, 29.30, 26.97, 22.63, 16.16, 14.05.